thats weird, I've got a ntsc console and all my isos are ntsc to the exeption of fatal frame 4 and most of them get a disc reading error or just show the intro screen, it desn't matter if ive got disabled "use Pal60" in the settings (not sure if it has any bearing)

I was replying to Chaoscode, but your detail was interesting, a guess launching a game makes it become the default iso until restart or something.

edit: yeah i can confirm that if you don't have a default iso set, the last launched game will appear in the Disc channel. Not sure how useful that is but it might mean that your wii os will log how much time you play; for me, it only logged how much time i played nsmb because it was set as default iso.